1. Field of the Invention
The present invention relates to methods for wellbore completion. More particularly, the invention relates to an apparatus for selectively translating a completion tool, such as an expander tool, downhole.
2. Description of the Related Art
Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a section of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus known in the art, the casing is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed or xe2x80x9chungxe2x80x9d off of the existing casing by the use of slips which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever decreasing diameter.
Apparatus and methods are emerging that permit tubulars to be expanded in situ. The apparatus typically includes expander tools which are fluid powered and are run into the wellbore on a working string. The hydraulic expander tools include radially expandable members which, through fluid pressure, are urged outward radially from the body of the expander tool and into contact with a tubular therearound. As sufficient pressure is generated on a piston surface behind these expansion members, the tubular being acted upon by the expansion tool is expanded past its point of elastic deformation. In this manner, the inner and outer diameter of the tubular is increased in the wellbore. By rotating the expander tool in the wellbore and/or moving the expander tool axially in the wellbore with the expansion member actuated, a tubular can be expanded into plastic deformation along a predetermined length in a wellbore.
Multiple uses for expandable tubulars are being discovered. For example, an intermediate string of casing can be hung off of a string of surface casing by expanding an upper portion of the intermediate string into frictional contact with the lower portion of surface casing therearound. This allows for the hanging of a string of casing without the need for a separate slip assembly as described above. Additional applications for the expansion of downhole tubulars exist. These include the use of an expandable sand screen, employment of an expandable seat for seating a diverter tool, and the use of an expandable seat for setting a packer.
There are problems associated with the expansion of tubulars. One problem particularly associated with the use of rotary expander tools is the likelihood of obtaining an uneven expansion of a tubular. In this respect, the inner diameter of the tubular that is expanded tends to initially assume the shape of the compliant rollers of the expander tool, including imperfections in the rollers. Moreover, as the working string is rotated from the surface, the expander tool may temporarily stick during expansion of a tubular, then turn quickly, and then stop again. This spring-type action in the working string further creates imperfections in the expansion job.
Another obstacle to smooth expansion relates to the phenomenon of pipe stretch. Those of ordinary skill in the art will understand that raising a working string a selected distance at the surface does not necessarily translate in the raising of a tool at the lower end of a working string by that same selected distance. The potential for pipe stretch is great during the process of expanding a tubular. Once the expander tool is actuated at a selected depth, an expanded profile is created within the expanded tubular. This profile creates an immediate obstacle to the raising or lowering of the expander tool. Merely raising the working string a few feet from the surface will not, in many instances, result in the raising of the expander tool; rather, it will only result in stretching of the working string. Applying further tensile force in order to unstick the expander tool may cause a sudden recoil, causing the expander tool to move uphole too quickly, leaving gaps in the tubular to be expanded.
The same problem exists in the context of pipe compression. In this respect, the lowering of the working string from the surface does not typically result in a reciprocal lowering of the expander tool at the bottom of the hole. This problem is exacerbated by rotational sticking, as discussed above. The overall result of these sticking problems is that the inner diameter of the expanded tubular may not have a uniform circumference.
There is a need, therefore, for an improved apparatus for expanding a portion of casing or other tubular within a wellbore. Further, there is a need for an apparatus which will aid in the expansion of a tubular downhole and which avoids the potential of pipe-stretch/pipe-compression by the working string. Correspondingly, there is a need for a method for expanding a tubular which avoids the risk of uneven expansion of the tubular caused by pipe-stretch incident to raising the working string. Still further, a need exists for an apparatus which will selectively translate a completion tool such as a rotary expander axially downhole without requiring that the working string be raised or lowered.
There is yet a further need for an apparatus which translates a rotary expander tool along a threaded shaft by rotation of the shaft.
The present invention provides an apparatus and method for selectively translating a completion tool, such as an expander tool, downhole. According to the present invention, an expansion assembly is introduced into a wellbore. The expansion assembly is lowered downhole on a working string. At the same time, the expansion assembly is releasably connected to the lower string of casing or other tubular to be expanded. In this way, the expandable tubular is lowered into the wellbore by the working string as well.
The expansion assembly first comprises a rotary expander tool. The expander tool includes compliant rollers which are expandable outwardly against the inner surface of the tubular upon actuation. The expansion assembly further comprises an elongated threaded body, such as an externally threaded shaft, aligned co-axially within the wellbore and connected to the expander tool. Rotation of the working string causes both the threaded shaft and the expander tool to rotate. The expansion assembly further comprises a nut member which is bearingly connected to an end of the expander tool. The nut member is stationary, meaning that it does not rotate within the expansion assembly. However, rotation of the threaded shaft causes the nut member to advance along the threads of the shaft upwardly or downwardly, depending upon the direction of rotation of the working string. This, in turn, causes the expander tool to be translated upwardly or downwardly within the wellbore. In this manner, the expander tool can be selectively raised or lowered without raising or lowering the working string itself.